Prestress tensioning jack

Abstract

The utility model relates to the technical field of prestress tensioning equipment, in particular to a prestress tensioning jack, which comprises an outer cylinder, a middle cylinder arranged in the outer cylinder, a first piston arranged at the bottom of the middle cylinder, a cylinder outlet oil port and a cylinder return oil port which are respectively arranged on the outer cylinder on two sides of the first piston, and an inner cylinder arranged in the middle cylinder, the inner cylinder is sleeved with the first piston in a sliding and sealing mode, a bottom shell is arranged at the bottom of the inner cylinder, and a pressurization mechanism is arranged on the bottom shell; the pressurizing mechanism comprises a bottom cylinder arranged below the outer cylinder, a second piston sleeved in the bottom cylinder in a sliding and sealing mode and a third piston sleeved in the outer cylinder in a sliding and sealing mode, the second piston and the third piston are of an integrated structure, the second piston and the third piston are both movably sleeved on the inner cylinder, and the inner cylinder, the second piston and the third piston form a conveying channel. The utility model provides a prestress tensioning jack which can widen the stress application range and enhance the stability of an anchoring system in the tensioning process, and is used for overcoming the defects in the prior art.

Description

Technical Field

[0001] This utility model relates to the technical field of prestressed tensioning equipment, specifically to a prestressed tensioning jack. Background Technology

[0002] A prestressed jack is a hydraulic jack specifically designed for tensioning prestressed tendons such as steel strands and reinforcing bars. Its working principle involves tensioning the prestressed tendons, inducing prestress in the concrete structure before it bears load, thus significantly improving the structure's crack resistance and load-bearing capacity. Therefore, prestressed jacks are widely used in bridge construction, building construction, tunnel engineering, and many other fields. Prestressed jacks belong to the through-hole type of hydraulic jack, with a unique structural design featuring a through-hole along the central axis. By passing the prestressed tendons through this through-hole and then using anchors to firmly anchor the jack to the tendons, the required stress can be effectively applied to the prestressed tendons. In actual use, prestressed jacks need to work in conjunction with a high-pressure oil pump. The high-pressure oil pump delivers high-pressure oil to the jack, while the internal hydraulic system converts this high-pressure oil into a powerful tensioning force. By utilizing this tensioning force, prestressing jacks can apply the necessary stress to the prestressing tendons passing through them, thereby achieving tensioning of the prestressing tendons. After the prestressing tendons are tensioned to the required degree, anchorages are needed to secure these stressed tendons, ensuring that the prestress is stably maintained on the tendons. Through this operational process, prestressing jacks apply prestress to the prestressing tendons.

[0003] In the field of prestressed concrete construction, handheld and pedestal-mounted jacks are two common types. Pedestal-mounted prestressed jacks are suitable for applications requiring stable support and large tension forces, playing a crucial role in the construction of large structures such as large bridges and high-rise buildings. However, pedestal-mounted jacks are difficult to use in confined spaces or complex environments with unstable support conditions due to their large size, making them difficult to mount onto the prestressing tendons. In contrast, handheld prestressed jacks, with their compact structure, portability, simple assembly, and suitability for use in various complex environments, are widely used in prestressed concrete construction projects such as highway bridges, railway bridges, hydropower dams, and high-rise buildings.

[0004] Handheld jacks are the preferred tool for construction workers due to their excellent portability and adaptability. However, because of their smaller size, handheld prestressing jacks can provide far less stress than pedestal jacks. In specific environments and working conditions with high tension design requirements, the stress applied by handheld jacks may not meet the design requirements. This can lead to increased stress amplitude in the structure under repeated loads, causing premature cracking and significant deflection, reducing the structure's service life, and even causing the anchor plates to loosen or dislodge within the anchor rings, thus affecting the overall safety of the building. Therefore, there is room for improvement in handheld jacks for prestressed construction. Optimizing the structure of handheld jacks, increasing their stress application range, and enhancing the stability of the anchoring system during tensioning are not only of significant practical importance for prestressed construction but also have undeniable value in improving project quality and ensuring building safety. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this utility model provides a prestressed tensioning jack that increases the range of applied stress and enhances the stability of the anchoring system during tensioning, thereby overcoming the deficiencies in existing technologies.

[0006] The technical solution adopted in this utility model is as follows: a prestressed tensioning jack, comprising an outer cylinder, a middle cylinder disposed within the outer cylinder, a first piston disposed at the bottom of the middle cylinder, and an outer cylinder on both sides of the first piston respectively provided with an outlet oil port and a return oil port. The middle cylinder is disposed within an inner cylinder, with the first piston slidably and sealingly fitted onto the inner cylinder. The bottom of the inner cylinder is provided with a bottom shell, and a pressure boosting mechanism is disposed on the bottom shell. The pressure boosting mechanism comprises a bottom cylinder disposed below the outer cylinder, a second piston slidably and sealingly fitted within the bottom cylinder, and a third piston slidably and sealingly fitted within the outer cylinder. The second and third pistons are an integral structure, and both the second and third pistons are movably fitted onto the inner cylinder. The inner cylinder, the second piston, and the third piston form a conveying channel. The outlet oil port is connected to the inner cavity of the outer cylinder through the inner cavity of the bottom cylinder and the conveying channel. A pressure relief hole is provided on the outer wall of the bottom cylinder, and the pressure relief hole is located above the second piston.

[0007] Preferably, a top pressure body is provided on the side of the inner cylinder away from the bottom shell. The top pressure body and the inner cylinder are an integral structure. A top pressure mechanism is provided on the top pressure body. The top pressure mechanism includes a spring provided in the top pressure body, an anchor ring provided at the end of the top pressure body away from the inner cylinder, and several clamping pieces movably fitted inside the anchor ring. The anchor ring is installed on the top pressure body. The inner cavity of the anchor ring adopts a conical groove structure. The outer shape of the several clamping pieces matches the inner cavity shape of the anchor ring. The several clamping pieces are all fixed inside the anchor ring by spring compression.

[0008] Preferably, a top anchor tube is provided on the side of the clamping plate away from the spring. The top anchor tube is movably fitted inside the anchor ring. One side of the top anchor tube is in contact with the clamping plate, and a top head is provided on the other side of the top anchor tube. The top anchor tube is connected to the middle cylinder through the top head. A pressure sleeve is fitted inside the spring. A pressure ring is provided at one end of the pressure sleeve. The pressure ring and the pressure sleeve are an integral structure. The pressure ring is located between the spring and the clamping plate. Both sides of the spring are in contact with the inner cylinder and the pressure ring, respectively.

[0009] Preferably, the top of the bottom cylinder is installed on the bottom of the outer cylinder, and the pressure relief hole is threaded with a cap. The cap has a fixing groove and a venting groove. The pressure relief hole is connected to the bottom cylinder through the venting groove. The fixing groove has a polygonal groove structure and is located on the side of the cap away from the inner cylinder.

[0010] Preferably, the third piston has a transverse hole and a through groove at the end away from the second piston. The transverse hole is opened laterally on the end face of the third piston, and the through groove adopts a circular groove structure. The through groove extends along the end face of the third piston toward the middle of the third piston. The through groove is connected to the conveying channel through the transverse hole. A sealing gasket is provided between the second piston and the bottom shell. The sealing gasket is installed on the bottom shell and the sealing gasket is fixedly fitted between the bottom cylinder and the inner cylinder. A sleeve groove is opened on the side of the sealing gasket near the second piston. The sleeve groove is opened in the middle of the end face of the sealing gasket.

[0011] Preferably, a transverse groove is provided on the outer cylinder above the return oil port. The transverse groove is located on the inner wall of the outer cylinder, and a sealing ring made of elastic material is interference-fitted into the transverse groove. The sealing ring is interference-fitted onto the middle cylinder.

[0012] Preferably, the outer cylinder is provided with a handle, one side of which is installed on the outer wall of the outer cylinder. The first piston is slidably sealed inside the outer cylinder. The first piston and the middle cylinder are an integral structure. The cylinder outlet is located between the bottom cylinder and the first piston.

[0013] The beneficial effects of this invention are as follows: First, the first piston installed inside the outer cylinder converts the pressure of the oil into a tensile force. A delivery channel is created between the inner cylinder and the second piston, allowing high-pressure oil to push the second piston towards the first piston, increasing the applied stress and thus improving the tensile effect. A third piston is slidably sealed inside the outer cylinder to prevent oil from flowing between the outer cylinder and the third piston, restricting oil delivery through the delivery channel. A pressure relief hole on the outer wall of the bottom cylinder connects the bottom cylinder above the second piston to the outside, preventing air pressure inside the outer cylinder from hindering the second piston from converting pressure into a tensile force, thereby improving the stability of the tensile effect.

[0014] Secondly, this invention utilizes a spring to move the clamping pieces closer to the anchor ring, thus anchoring the prestressing tendons inserted into the inner cylinder to the anchor ring. This allows the invention to be assembled onto the prestressing tendons. A top anchor pipe connected to the middle cylinder allows the middle cylinder to move the top anchor pipe, which in turn moves the clamping pieces away from the anchor ring, releasing the anchorage between the prestressing tendons and the anchor ring. This facilitates removal of the invention from the prestressing tendons, reducing the difficulty of assembling it with them. Furthermore, the pressure ring and pressure sleeve ensure that the clamping pieces are evenly subjected to the spring force, preventing them from shifting during tensioning.

[0015] Furthermore, this invention, through the design of the cap and the venting groove on the cap, prevents visible suspended impurities such as sand and dust from entering the pressure relief hole, thereby preventing these impurities from wearing down the second and third pistons. The polygonal groove on the side of the cap away from the inner cylinder facilitates the use of a polygonal screwdriver to turn the cap, making it easy to install and remove. The transverse hole and through-slot on the third piston facilitate the delivery of oil to the delivery channel, enabling control of the pressurization mechanism. The sealing gasket seals the space between the inner and bottom cylinders, preventing oil leakage from the chamber between them.

[0016] Furthermore, this invention features a transverse groove on the inner wall of the outer cylinder to limit the sealing ring. The sealing ring is interference-fitted onto the middle cylinder to seal the space between the outer and middle cylinders, preventing oil leakage from the chambers of the outer and middle cylinders. Additionally, this invention includes a handle for easy carrying. Attached Figure Description

[0017] Figure 1 This is a three-dimensional schematic diagram of the present invention.

[0018] Figure 2 This is a cross-sectional view of the present invention.

[0019] Figure 3 for Figure 2 Enlarged diagram of point A in the middle.

[0020] Figure 4 for Figure 2 Enlarged diagram of point B in the middle.

[0021] Figure 5 This is an exploded view of the assembly of the spring, pressure sleeve, clamping plate, and anchor ring in this utility model.

[0022] Figure 6 This is a schematic diagram of the structure of the cap in this utility model.

[0023] Figure 7 This is a schematic diagram of the assembly of the second piston and the third piston in this utility model. Detailed Implementation

[0024] like Figures 1 to 7 As shown, a prestressed tensioning jack includes an outer cylinder 1, a middle cylinder 2 inside the outer cylinder 1, a first piston 3 at the bottom of the middle cylinder 2, and an oil outlet 4 and a return oil outlet 5 on both sides of the outer cylinder 1. The first piston 3 is slidably and sealingly fitted inside the outer cylinder 1. An inner cylinder 6 is located inside the middle cylinder 2, and the first piston 3 is slidably and sealingly fitted onto the inner cylinder 6. A bottom shell 7 is located at the bottom of the inner cylinder 6, and a pressurizing mechanism is located on the bottom shell 7. The pressurizing mechanism includes a bottom cylinder 8 located below the outer cylinder 1, a second piston 9 slidably and sealingly fitted inside the bottom cylinder 8, and a third piston 10 slidably and sealingly fitted inside the outer cylinder 1. The second piston 9 and the third piston 10 are an integral structure, and both the second piston 9 and the third piston 10 are movably fitted onto the inner cylinder 6. The inner cylinder 6, the second piston 9, and the third piston 10 form a conveying channel 11. The oil outlet 4 connects to the inner cylinder 1 through the inner cavity of the bottom cylinder 8 and the conveying channel 11. The chambers are connected; the oil pump is connected to the outlet oil port 4, so that the oil is delivered to the outer cylinder 1 below the first piston 3, the delivery channel 11 and the bottom cylinder 8. As the oil pressure continues to increase, the pressure on the outer cylinder 1 and the bottom cylinder 8 also continues to increase, thereby pushing the first piston 3 and the middle cylinder 2 to move along the inner wall of the outer cylinder 1 for tensioning. If pressurization is required, the oil pressure is continuously increased, so that the oil entering the outer cylinder 1 pushes the second piston 9 and the third piston 10 to move. The oil between the third piston 10 and the first piston 3 transmits force to squeeze the first piston 3 and the middle cylinder 2, thereby increasing the tensioning force and improving the tensioning effect of this utility model. The bottom cylinder 8 has a pressure relief hole 12 on its outer wall, which is located above the second piston 9, so that the bottom cylinder 8 above the second piston 9 is connected to the outside, so as to avoid the air pressure in the outer cylinder 1 from affecting the tensioning operation.

[0025] In this embodiment, a top pressure body 13 is provided on the side of the inner cylinder 6 away from the bottom shell 7. The top pressure body 13 and the inner cylinder 6 are an integral structure. A top pressure mechanism is provided on the top pressure body 13. The top pressure mechanism includes a spring 14 provided inside the top pressure body 13, an anchor ring 15 provided at the end of the top pressure body 13 away from the inner cylinder 6, and several clamping pieces 16 movably fitted inside the anchor ring 15. The anchor ring 15 is installed on the top pressure body 13. The inner cavity of the anchor ring 15 adopts a conical groove structure. The outer shape of the several clamping pieces 16 matches the inner cavity shape of the anchor ring 15. The several clamping pieces 16 are all pressed and fixed inside the anchor ring 15 by the spring 14. The prestressed tendons that penetrate into the inner cylinder 6 are anchored to the anchor ring 15 by the clamping pieces 16, so as to clamp and fix the prestressed tendons to this utility model.

[0026] Specifically, a top anchor tube 17 is provided on the side of the clamping plate 16 away from the spring 14. The top anchor tube 17 is movably fitted inside the anchor ring 15. One side of the top anchor tube 17 is in contact with the clamping plate 16, and the other side of the top anchor tube 17 is provided with a top head 18. The top anchor tube 17 is connected to the middle cylinder 2 through the top head 18. The movement of the middle cylinder 2 can drive the top anchor tube 17 and the top head 18 to move. Under the action of the spring 14 pressing the clamping plate 16, the clamping plate 16 is controlled to move in or out of the anchor ring 15. When oil is applied to the cylinder oil port 4, the middle cylinder 2 drives the top anchor tube 17 to move away from the clamping plate 16. Under the action of the spring 14, the clamping plate 16 moves into the anchor ring 15, thereby allowing the prestressing tendon to pass through the clamping plate 16. 6. The anchor is held in place on the anchor ring 15. When oil is applied to the return cylinder oil port 5, the middle cylinder 2 drives the top anchor pipe 17 to move towards the clamping piece 16, so as to use the top anchor pipe 17 to squeeze the clamping piece 16, thereby releasing the anchor between the prestressing tendon and the anchor ring 15, so as to facilitate the removal of this utility model from the prestressing tendon. The spring 14 is fitted with a pressure sleeve 19. One end of the pressure sleeve 19 is provided with a pressure ring 20. The pressure ring 20 and the pressure sleeve 19 are an integral structure. The pressure ring 20 is located between the spring 14 and the clamping piece 16. The two sides of the spring 14 are in contact with the inner cylinder 6 and the pressure ring 20 respectively. The pressure ring 20 is used to make the elastic force of the spring 14 on several clamping pieces 16 uniform, thereby preventing the clamping pieces 16 from shifting during the tensioning process.

[0027] Please refer to Figure 3 and 5 The top of the bottom cylinder 8 is installed on the bottom of the outer cylinder 1. The pressure relief hole 12 is threaded with a cover 21. The cover 21 is provided with a fixing groove 22 and a venting groove 23. The pressure relief hole 12 is connected to the bottom cylinder 8 through the venting groove 23. The width of the venting groove 23 is no more than 0.1mm. Since the diameter of visible suspended impurities such as sand and dust is generally greater than 0.1mm, this prevents visible suspended impurities from entering the pressure relief hole 12. The fixing groove 22 adopts a polygonal groove structure. The fixing groove 22 is opened on the side of the cover 21 away from the inner cylinder 6. The cover 21 can be installed and removed by inserting a polygonal screwdriver into the fixing groove 22 and turning it.

[0028] In this embodiment, the third piston 10 is provided with a transverse hole 24 and a through groove 25 at the end away from the second piston 9. The transverse hole 24 is opened laterally on the end face of the third piston 10. The through groove 25 adopts a circular groove structure and extends along the end face of the third piston 10 toward the middle of the third piston 10. The through groove 25 is connected to the conveying channel 11 through the transverse hole 24 to facilitate the conveying of oil into the conveying channel 11 through the through groove 25 and the transverse hole 24. A sealing gasket 26 is provided between the second piston 9 and the bottom shell 7. The sealing gasket 26 is installed on the bottom shell 7 and is fixedly sealed between the bottom cylinder 8 and the inner cylinder 6 to prevent oil from leaking out from the bottom end of the bottom cylinder 8. A sleeve groove 27 is provided on the side of the sealing gasket 26 near the second piston 9. The sleeve groove 27 is opened in the middle of the end face of the sealing gasket 26 so that oil can be used to apply pressure to the bottom surface of the second piston 9.

[0029] Please participate again. Figure 3 A transverse groove 28 is provided on the outer cylinder 1 above the return oil port 5. The transverse groove 28 is provided on the inner wall of the outer cylinder 1. A sealing ring 29 made of elastic material is interference fitted inside the transverse groove 28. The sealing ring 29 is interference fitted on the middle cylinder 2, thereby sealing the inner cavity of the outer cylinder 1 and preventing oil from leaking out from the top of the outer cylinder 1.

[0030] Please refer to it again. Figure 1 The outer cylinder 1 is provided with a handle 30, one side of which is installed on the outer wall of the outer cylinder 1. By holding the handle 30, it is convenient to carry this utility model. The first piston 3 is slidably sealed inside the outer cylinder 1. The first piston 3 and the middle cylinder 2 are an integral structure. The oil outlet 4 is located between the bottom cylinder 8 and the first piston 3, so as to facilitate the addition of oil to the bottom cylinder 8 through the oil outlet 4.

[0031] According to the above-mentioned method of using prestressed tensioning jacks, such as Figure 1-7As shown, the process includes the following steps: S1, Take out the oil pump and prestressing tension jack, place the oil pump on one side of the prestressing tension jack, then connect the oil outlet port 4 of the cylinder to the oil outlet port of the oil pump using a high-pressure hose, and connect the oil return port 5 of the cylinder to the oil return port of the oil pump using another high-pressure hose to complete the assembly of the oil pump and the prestressing tension jack; S2, Control the operating valve of the oil pump to move the middle cylinder 2 toward the bottom cylinder 8, thereby driving the top anchor pipe 17 toward the clamping plate 16, so as to drive the clamping plate 16 toward... Move away from anchor ring 15 to complete the preparation work; S3, move the oil pump and prestressing tensioning jack together to the working area, insert the prestressing tendon to be tensioned into the inner cylinder 6, and make the top head 18 contact the anchor cable and anchor installed on the prestressing tendon. By controlling the operating valve of the oil pump, the oil is delivered to the outlet oil port 4, thereby pushing the first piston 3, the middle cylinder 2, the top anchor pipe 17 and the top head 18 to move along the inner wall of the outer cylinder 1 away from the bottom cylinder 8. At the same time, under the squeezing action of the spring 14, S4. The pressure ring 20 and several clamping pieces 16 are pushed to move toward the anchor ring 15 to anchor the prestressed tendon into the anchor ring 15, thereby applying a tensioning force to the prestressed tendon; S5. As the oil pressure delivered by the oil pump continues to increase, the oil entering the outer cylinder 1 pushes the second piston 9 and the third piston 10 toward the first piston 3, thereby applying a squeezing force to the first piston 3 and the middle cylinder 2 to increase the tensioning force of the prestressed tendon anchor, and thus improve the tensioning effect of the prestressed tendon; S6. After the prestressed tendon tensioning is completed, the operating valve of the oil pump is reversed, causing the oil to move toward the anchor ring 15. The oil is pumped into the return cylinder port 5, pushing the first piston 3, the middle cylinder 2, the top anchor tube 17 and the top head 18 to reset. This causes the top anchor tube 17 to move closer to the clamping plate 16 and squeezes the clamping plate 16 to move away from the anchor ring 15, thereby releasing the anchoring of the prestressed tendon. At the same time, the first piston 3 drives the second piston 9 and the third piston to reset. S6. The operating valve of the oil pump is closed, and the prestressing tensioning jack is removed from the prestressed tendon so that the prestressing tensioning jack and oil pump can be used again to tension the prestressed tendon.

[0032] It should be noted that after the oil pump and prestressed tensioning jack are assembled, the hydraulic system between the oil pump and the prestressed tensioning jack should be checked for leaks. The oil pump's operating valve should be controlled to supply oil to the outlet port 4 or return port 5. Observe the oil pump, prestressed tensioning jack, and high-pressure hose for any leaks. If a leak is found, first close the oil pump's operating valve, and then repair the leaking area to ensure the safety of using the oil pump and prestressed tensioning jack.

[0033] In this embodiment, the first piston 3 installed inside the outer cylinder 1 converts the pressure of the oil into a tensioning force. A delivery channel 11 is created between the inner cylinder 6 and the second piston 9, allowing high-pressure oil to push the second piston 9 towards the first piston 3, increasing the applied stress and thus improving the tensioning effect. A third piston 10 is slidably sealed inside the outer cylinder 1 to prevent oil from flowing between the outer cylinder 1 and the third piston 10, restricting oil delivery through the delivery channel 11. A pressure relief hole on the outer wall of the bottom cylinder 8 connects the bottom cylinder 8 above the second piston 9 to the outside environment, preventing air pressure inside the outer cylinder from hindering the second piston 2 from converting pressure into a tensioning force, thereby improving the stability of the tensioning effect.

[0034] The embodiments described above are merely preferred embodiments of this utility model and are not intended to limit the scope of implementation of this utility model. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the patent claims of this utility model should be included within the scope of the patent application of this utility model.

Claims

1. A prestressed tensioning jack, comprising an outer cylinder (1), a middle cylinder (2) disposed inside the outer cylinder (1), a first piston (3) disposed at the bottom of the middle cylinder (2), and an outlet oil port (4) and a return oil port (5) respectively disposed on both sides of the outer cylinder (1) of the first piston (3), characterized in that: The inner cylinder (6) is arranged in the middle cylinder (2), the first piston (3) is slidably and sealingly arranged in the inner cylinder (6), the bottom of the inner cylinder (6) is provided with a bottom shell (7), and the bottom shell (7) is provided with a supercharging mechanism. The supercharging mechanism comprises a bottom cylinder (8) arranged below the outer cylinder (1), a second piston (9) slidably and sealingly arranged in the bottom cylinder (8), and a third piston (10) slidably and sealingly arranged in the outer cylinder (1), the second piston (9) and the third piston (10) are integrated, the second piston (9) and the third piston (10) are both slidably and sealingly arranged in the inner cylinder (6), the inner cylinder (6), the second piston (9) and the third piston (10) form a conveying channel (11), and the cylinder oil outlet (4) is connected with the inner cavity of the outer cylinder (1) through the inner cavity of the bottom cylinder (8) and the conveying channel (11). The outer wall of the bottom cylinder (8) is provided with a pressure relief hole (12), and the pressure relief hole (12) is located above the second piston (9).

2. The pre-stressing tensioning jack according to claim 1, characterized in that: The inner cylinder (6) is provided with a top pressing body (13) on the side away from the bottom shell (7), the top pressing body (13) is integrated with the inner cylinder (6), and the top pressing body (13) is provided with a top pressing mechanism. The top pressing mechanism comprises a spring (14) arranged in the top pressing body (13), an anchor ring (15) arranged at one end of the top pressing body (13) away from the inner cylinder (6), and a plurality of clamping pieces (16) slidably and sealingly arranged in the anchor ring (15), the anchor ring (15) is installed on the top pressing body (13), the inner cavity of the anchor ring (15) is in a conical groove shape, the outer shape of the plurality of clamping pieces (16) is consistent with the shape of the inner cavity of the anchor ring (15), and the plurality of clamping pieces (16) are fixed in the anchor ring (15) by the spring (14).

3. The pre-stressing tensioning jack according to claim 2, characterized in that: The clamping piece (16) is provided with a top anchor pipe (17) on the side away from the spring (14), the top anchor pipe (17) is slidably and sealingly arranged in the anchor ring (15), one side of the top anchor pipe (17) is in contact with the clamping piece (16), the other side of the top anchor pipe (17) is provided with a top head (18), and the top anchor pipe (17) is connected with the middle cylinder (2) through the top head (18); the spring (14) is sleeved with a pressing sleeve (19), one end of the pressing sleeve (19) is provided with a pressing ring (20), the pressing ring (20) is integrated with the pressing sleeve (19), the pressing ring (20) is located between the spring (14) and the clamping piece (16), and the two sides of the spring (14) are in contact with the inner cylinder (6) and the pressing ring (20) respectively.

4. The pre-stressing tensioning jack according to claim 1, characterized in that: The bottom of the bottom cylinder (8) is installed on the bottom of the outer cylinder (1), the pressure relief hole (12) is threadedly sleeved with a cover (21), the cover (21) is provided with a fixing groove (22) and a ventilation groove (23) respectively, the pressure relief hole (12) is connected with the bottom cylinder (8) through the ventilation groove (23), the fixing groove (22) is in a polygonal groove shape, and the fixing groove (22) is arranged on the side of the cover (21) away from the inner cylinder (6).

5. The pre-stressing tensioning jack as claimed in claim 1, wherein: The third piston (10) is provided with a transverse hole (24) and a through groove (25) at one end away from the second piston (9), the transverse hole (24) is transversely provided on the end face of the third piston (10), the through groove (25) is in the form of a circular ring groove, the through groove (25) extends along the end face of the third piston (10) towards the middle part of the third piston (10), the through groove (25) is connected with the conveying channel (11) through the transverse hole (24), the second piston (9) and the bottom shell (7) are provided with a sealing gasket (26), the sealing gasket (26) is installed on the bottom shell (7), the sealing gasket (26) is fixedly and sealingly sleeved between the bottom cylinder (8) and the inner cylinder (6), the side of the sealing gasket (26) close to the second piston (9) is provided with a sleeve groove (27), the sleeve groove (27) is provided in the middle part of the end face of the sealing gasket (26).

6. The pre-stressing tensioning jack according to claim 1, characterized in that: The outer cylinder (1) above the return cylinder oil port (5) is provided with a transverse groove (28), the transverse groove (28) is provided on the inner wall of the outer cylinder (1), the transverse groove (28) is provided with a sealing ring (29) made of elastic material in an interference fit, and the sealing ring (29) is provided in an interference fit on the middle cylinder (2).

7. The pre-stressing tensioning jack according to claim 1, characterized in that: The outer cylinder (1) is provided with a handle (30), one side of the handle (30) is installed on the outer wall of the outer cylinder (1), the first piston (3) is slidingly and sealingly sleeved in the outer cylinder (1), the first piston (3) and the middle cylinder (2) are in an integral structure, and the cylinder oil outlet (4) is located between the bottom cylinder (8) and the first piston (3).

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